1. Field
The disclosure relates to a method for growing single crystals, and more particularly to a method for growing single crystals by making the average size of matrix grains of polycrystalline bodies to more than a critical size at which an abnormal, exaggerated or discontinuous grain growth ends and no abnormal grains exist [or the number density (ND) of the abnormal grains (number of abnormal grains/unit area) become zero], and less than twice the critical size, thereby enhancing growth of a seed single crystal into a polycrystalline body without any impingement between a growing seed single crystal and abnormal grains.
2. Background of the Related Art
The single crystals are generally manufactured by using a melting process. Accordingly, a general method for single crystal growth using the melting process is referred to as a Liquid-State Single Crystal Growth (LSCG) method.
Contrary to the general liquid-state single crystal growth method, a method for producing the single crystals by using a grain growth of matrix grains without the melting process of their major components is referred to as a Solid-State Single Crystal Growth (SSCG) method. Herein, the grain growth may occur during heat treatment of the polycrystalline bodies.
The SSCG method has been suggested since the 1950's and was practiced in producing single crystals of a metal, which is limited only a few types. It is, however, reported that when the single crystals are produced by the grain growth in oxide materials, the method has a difficulty in manufacturing single crystals big enough for practical use from the oxide.
Meanwhile, there has been made an attempt to obtain single crystals by heat-treating polycrystalline bodies of ferrite, barium titanate (BaTiO3), aluminum oxide (Al2O3), PMN-PT, etc. through the solid-state single crystal growth method. This is a method for growing seed single crystals in polycrystalline bodies, which involves sintering powder-molded bodies impregnated with seed single crystals or forming an interface between the polycrystalline body and the seed single crystal, followed by heat treatment. However, the method is not suitable to preparing single crystals big enough for practical uses such as several tens mm.